1. Field of the Invention
The present invention generally relates to wireless communication technology and more particularly to a neighbor cell synchronization method and apparatus for a mobile communication unit.
2. Description of the Prior Art
Wireless mobile communication systems have become more and more popular in recent years. In addition to be used as the telecommunication system for voice communication, they may also be used as the transmitting media for digital data. A wireless mobile communication system is generally in charge of the communication between Mobile Communication Units, such as cell phones, and Base Stations. The communication range covered by a base station is called a “cell”. A single mobile communication unit may lie in an area reachable by several cells.
A mobile communication unit must always keep in synchronization with reachable cells, or neighbor cells, so as to guarantee that backup communication channels to the telecommunication system are available all the time. The synchronization herein means identifying the time difference between the mobile communication unit and the neighbor cells such that the mobile communication unit may rapidly get BSIC (Base Station Identity Code) and other synchronizing information necessary for handover between base stations.
The GSM (Global System for Mobile Communication) protocol uses TDMA (Time-Division Multiple-Access) mechanism which divides every single frame lasting for 4.615 microseconds into 8 time slots. Each time slot may carry user information or control information. According to the type of the carried information, different logic channel may be defined on a time slot. Basically, a logic channel which carries user information is called a TCH (Traffic Channel) and a logic channel which carries control information is called a Control Channel. Typical control channels include FCCHs (Frequency Correction Channels), SCHs (Synchronization Channels), BCCHs (Broadcast Control Channels) and CCCHs (Common Control Channels). The BSIC information mentioned above lies in SCH. The neighbor cell synchronization for a mobile communication unit aims to search and decode the FCCHs and SCHs of neighbor cells.
The environments in which a mobile communication unit is located may have a plurality of neighbor cells. For example, the GSM protocol requires that a mobile communication unit must handle up to 6 neighbor cells and complete scanning all neighbor cells within 30 seconds. In other words, the synchronization of a single neighbor cell must be completed within 2 to 5 seconds. A mobile communication unit toggles between the neighbor cell synchronization status and the normal status and consumes a lot of electric power for that. In view of the foregoing, there is a need to provide an efficient neighbor cell synchronization method to rapidly monitor the neighbor cells on the premise of economic electric power consumption.